Apparatus for accelerating response time of active mass damper earthquake attenuator
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an apparatus for positively suppressing vibrations of building structures caused by such external forces as earthquakes and winds. 
     2. Description of the prior art 
     The present inventors have been invented an apparatus for positively suppressing vibrations of a building, which comprises an additional mass and an actuator and is provided on the top or the like of the building to apply, when the building experiences external forces of an earthquake or winds, a force tending to suppress the vibrations to the building from the reaction force of a weight as the additional mass produced through control of the operation of the actuator (as disclosed in Japanese Patent Laid-open Publications Nos. 62-268478 and 63-78974). 
     FIG. 1 illustrates the outline of the positive vibration suppression apparatus. On the top of a building 1, for example, a weight 2 is provided as an additional mass such that it is substantially separated from the building 1, and an actuator 3 is interposed between the weight 2 and a portion of the building 1. When vibrations of the building 1 are produced by an earthquake or winds, a sensor 4a provided in the building 1 senses the vibrations and provides a signal to a control circuit, which in turn supplies an output signal corresponding to the vibrations to a servo valve connected to the actuator 3 to control the actuator 3. Further, another sensor 4b may be provided on the side of the actuator 3 to effect feedback control of the movement of the actuator 3. While the above control is based on a closed loop control, it is also possible to measure a response of the building through analysis of earthquake waves supplied from wide and narrow bandwidth seismometers and combine the result of the analysis with an opened loop control. 
     However, a delay with respect to the signal in the operation time is produced in a mechanical part of the apparatus. Such a time delay should be reduced. 
     Further, earthquakes and winds are natural phenomena, and their scales can not be forecast when designing the apparatus. Therefore, where the maximum performance of the apparatus is determined with respect to frequently occurring medium scale earthquakes and typhoons with wind velocities of 15 m/sec. or less, it is necessary to prevent an excessive load above the capacity of the apparatus from being applied to the apparatus at the time of occurrence of a large scale earthquake. Thus, it is necessary to suppress a control force with respect to vibrations when large scale vibrations of the building take place. 
     Further, nobody can tell when an earthquake takes place, and the apparatus should be rendered operative as soon as an earthquake occurs. Further, it takes time until a steady operation state of an oil hydraulic system sets in after the start. This means that it is necessary to have the system warmed up by starting it to be ready for the occurrence of an earthquake at all time. For this reason, the system requires extreme running expenditures such as electric power expenditures. In addition, the life of the system is not so long. 
     Further, strong winds do not appear at all time, so that a large capacity electric motor need not be held operative at all time. 
     Further, the weight 2, which is made of steel with a mass of about 1/100 of the weight of the building, should be such that a force of the actuator 3 is smoothly transmitted to the weight. Further, the installation space is desirably as small as possible. 
     Further, the actuator 3 desirably operates at a comparatively high speed and has a large capacity, and is desirably constituted by an oil hydraulic cylinder or the like to realize a large stroke apparatus. In this case, it is important to secure the oil hydraulic cylinder installation space inclusive of the space for the stroke. 
     Further, since the weight 2 has a considerably large mass, it is necessary to reduce the influence of frictional forces as much as possible to obtain efficient and reliable vibration suppression. 
     Where an oil hydraulic cylinder is used for the actuator 3, the direction of control is limited, that is, it is impossible to suppress the vibrations of the building in certain directions although the vibrations in other directions can be suppressed. 
     Depending on the design of the building, it is usually possible to obtain a comparatively large effect through control only in one direction. However, externally applied forces due to earthquakes and winds are uncertain forces, and, in an eccentric building or the like, further effective vibration suppression can be obtained by suppressing the torsional component of vibrations. 
     Further, in high story or ultra-high story buildings, the secondary vibration component is often large. Therefore, it is possible to improve the vibration suppression effect by suppressing the secondary vibration component. 
     SUMMARY OF THE INVENTION 
     A positive vibration suppression apparatus according to the present invention basically provides a control force converse to vibrating force and proportional to the speed of vibrations. More specifically, a signal from vibration sensor means provided on or in a building is amplified by an amplifier to obtain a control signal to control an actuator, and a reaction force of a weight in the actuator is applied as the control force to the building to suppress vibration thereof. 
     According to one aspect of the invention, the building and weight are provided with respective vibration sensor means for sensing their vibrations, and amplifying circuits are provided in parallel to amplify response signals from the respective vibration sensor means. Mechanical delay can be compensated for by providing phase control means in the amplifying circuits. The phase control means includes an integrating circuit to cause a phase shift of 90 degrees so that it can control a phase within a range of 0 to 90 degrees. It is thus possible to control the phase (within a range of ±180 degrees) according to the delay in mechanical part. Further, the amplifying circuit for amplifying the response signal from the building side vibration sensor means is provided with an automatic gain control circuit for controlling the signal level. Further, another automatic gain control circuit is provided for controlling the output level of a resultant signal obtained from the two amplifying circuits on the building side and on the weight side. 
     If acceleration gauges are used as vibration sensor means, it is possible to sense very small vibrations and higher order vibrations. In this case, the phase delay can be reasily compensated for to permit phase control of the actuator with in cooperation with the phase control means noted above. 
     As shown above, according to the invention it is possible to compensate for the mechanical time delay by the provision of phase control means in the amplifying circuits. Further, it is possible to control the level of a signal when combining the building side response signal with the amplified weight side response signal by providing the automatic gain control circuit in the amplifying circuit for amplifying the building side response signal. Thus, when vibrations of the building are not so great, it is possible to obtain control according to the amplitude of vibrations for the amplification factor for the building side response signal is large. When the vibrations of the building are increased, the amplification factor of the building side response signal is reduced, and the factor of contribution of the movement on the weight side to the control is increased. At any rate, the vibration suppression apparatus effects control in a fixed capacity range irrespective of vibrations of the building. Therefore, while the vibrations are great, the weight is moved substantially in unison with the building (i.e., it is substantially stationary with respect to the building) and does not receive any substantial large force, and the safety of the apparatus can be ensured. When the vibrations of the building are reduced with attenuation of an earthquake, the amplification factor for the building side response signal is increased by the action of the automatic gain control circuit, so that it is possible to obtain control for effectively suppressing the vibrations of the building. Further, with respect to the output of the resultant signal the output level thereof is further amplified by the automatic gain control circuit. Therefore, the vibration suppression apparatus will not excessively operate for excessive vibrations of the building. In other words, vibrations of the building in excess of the capacity of the vibration suppression apparatus are controlled within the capacity of the vibration suppression apparatus, and with respect to greater vibrations the relative movements of the weight and building are reduced, thus ensuring the safety of the apparatus. 
     It is possible to greatly extend the scope of application by permitting the vibrations of the building to be suppressed by combining the vibration suppression apparatus with vibration-proof structure, vibration absorbers and other vibration suppression apparatuses. 
     As an oil hydraulic pressure source of the positive vibration suppression apparatus, a small size oil hydraulic pump connected to a small size electric motor, a large size oil hydraulic pump connected to a large size electric motor and a large capacity accumulator are provided in parallel. Normally, only the small size electric motor is held operative to store oil hydraulic pressure in the accumulator by using the small size oil hydraulic pump as the oil hydraulic pressure source to hold the apparatus in a warmed-up state at all time. In an initial stage of an earthquake, necessary oil hydraulic pressure is supplied from the accumulator provided in parallel with the oil hydraulic pump. During this time, the large size electric motor is started to operate the large size oil hydraulic pump for supplying necessary oil hydraulic pressure in a final stage of the earthquake. Thus, an economical and stable oil hydraulic pressure source can be provided. 
     When an earthquake occurs, the large size electric motor is started by an electric signal transmitted from the control circuit of the positive vibration suppression apparatus to operate the large size oil hydraulic pump to effect warming-up of the apparatus while the accumulator is supplying oil hydraulic pressure necessary for the initial stage of the earthquake. The large size oil hydraulic pump commences supply of the oil hydraulic pressure by the time, when the pressure of the accumulator turns to be reduced. When strong winds are produced, the large size electric motor is started by an electric signal transmitted from the control circuit of the positive vibration suppression apparatus to operate the large size oil hydraulic pump as oil hydraulic pressure source, thereby enabling the operation of the apparatus. The large size pump is adapted to be supplied with pressure load when and only when it is required to do so through a pressure regulator valve or the like which is operable by pressure sensor means such as a pressure switch for sensing reduction of the oil hydraulic pressure of the accumulator, so that power of the motor can be consumed without waste. 
     In a different aspect of the invention, an oil hydraulic cylinder, with which a large stroke can be comparatively easily obtained, is used as the actuator, and the center of the oil hydraulic cylinder is supported by a pin on the gravitational axis of the weight via a center trunion or the like. The piston of the oil hydraulic cylinder has its free end in pin contact with a securing section of the building through a clevis or the like. Since the weight of the oil hydraulic cylinder is set on the weight, there is no need of securing an installation space of the oil hydraulic cylinder separately from the weight, so that the entire length of the mechanical part of the vibration suppression apparatus can be reduced. Further, since the center of the oil hydraulic cylinder is supported by a pin at a position on the gravitational axis of the weight, smooth transmission of force can be obtained compared to the case where the center of the oil hydraulic cylinder is connected to an end of the weight. Further, since the free end of the oil hydraulic cylinder is in pin contact, when the weight is suspended as will be described later, it is possible to absorb the vertical movement of the weight produced with horizontal movement thereof to permit stable transmission of force. 
     Further, by forming the weight such as to have a shape having a channel-shaped profile of a section perpendicular to the axial direction of the oil hydraulic cylinder, it is possible to arrange such that the axis of the oil hydraulic cylinder passes through the centroid of the weight, thus permitting smooth transmission of the force. The weight has a mass of about 1/100 of the mass of the building, and it is suitably made of such metal as steel or lead from the consideration of the space factor. 
     In order to minimize the mechanical time delay by causing momentary operation of the vibration suppression apparatus with respect to earthquake vibrations, it is necessary to reduce the friction in the mechanical part of the apparatus as much as possible. To this end, it is desired to suspend the weight via a hanging member such as wires. For installation, a steel frame is built on the top of or in the building, and the weight is suspended from the frame via the hanging member. The handing member suitably used includes wire ropes, PC steel wires or piano wires, and the weight is preferably suspended at a plurality of points, for instance, four or eight points, to remove the rotation of the weight. Further, it is desired to use pulleys as much as possible to preclude the influence of frictional force of the support. Further, compared to a method for supporting the weight with a roller or a method for causing the weight to roll along guide rails, the influence of the friction can be extremely minimized, and also even very small vibrations can be controlled. Further, buffers may be applied to the underside of the weight to cope with an accident in case where the weight is suspended. Further, it is desired to provide a guide to avoid torsional vibrations of the weight. 
     In a further aspect of the invention, a plurality of vibration suppression apparatuses as above are provided on or in the building to be controlled to suppress complicated vibrations of the building by simultaneously controlling the plurality of vibration suppression apparatuses. These vibration suppression apparatuses may utilize a common oil hydraulic pressure source to simplify the equipment. 
     More specifically, it is possible to obtain control conforming to the plane shape of building through control of vibrations in perpendicular directions with two vibration suppression apparatuses (see FIG. 5). Further, when it is intended to control vibrations in a particular direction, a main vibration suppression apparatus is installed at the center of the plane of the building, and an auxiliary vibration suppression apparatus is installed at an end of the plane of the building such that it extends in the same direction as the main vibration suppression apparatus for controlling the torsional component of vibrations of the building (see FIG. 6). Further, for a high story or ultra-high story building an auxiliary vibration suppression apparatus may be provided on a floor constituting the node of secondary vibration mode in addition to a main vibration suppression apparatus provided on the top of the building for simultaneously controlling the two apparatuses to control the secondary vibration component of the building with the auxiliary vibration suppression apparatus (see FIG. 7). 
     OBJECTS OF THE INVENTION 
     An object of the present invention is to provide an apparatus for positively suppressing vibrations of building structures, in which a control signal generating circuit for controlling the operation of an actuator such as an oil hydraulic cylinder is provided with phase control means to permit compensation of mechanical time delay with respect to the operation of the actuator. 
     Another object of the invention is to provide, in case where the maximum performance of the vibration suppression apparatus is determined in consideration of frequently occurring medium scale earthquakes as a subject, an amplifying circuit for amplifying a building side response signal with an automatic gain control circuit, for preventing excessive operation of the apparatus at the time of occurrence of large scale earthquakes to maintain the safety of the apparatus. 
     A further object of the invention is to provide an economical vibration suppression apparatus, in which an oil hydraulic apparatus for generating great control force is combined with an electric control circuit to effectively suppress vibrations of a building, and also a small size electric motor and a small size pump which are operated at all time are combined with a large size electric motor and a large size pump when and only when effecting control with respect to an earthquake or winds, so that the apparatus can be held warmed up at all time and can immediate start oil hydraulic control, permit control without application of any great load at the time of rise of the large size electric motor, consumes low power, requires low running cost and obtain a long-life and economical vibration suppression apparatus. 
     A further object of the invention is to provide a vibration suppression apparatus, which has a compact construction and permits smooth transmission of force with the point of application of force of an oil hydraulic cylinder and centroid of the weight coincident. 
     A still further object of the invention is to provide a vibration suppression apparatus, in which the weight is suspended to reduce influence of friction, eliminate rotation of the suspended weight and permit effective control. 
     A yet further object of the invention is to provide a vibration suppression apparatus, which is simple in the construction of the mechanical part and can be installed in the existing building. 
     A yet further object of the invention is to provide a method for suppressing vibrations, in which a plurality of vibration suppression apparatuses are controlled at the same time to permit control of vibrations in two perpendicular directions, control of torsional vibration component and control of secondary vibration component. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects and features of the invention will become apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings, in which: 
     FIG. 1 is a view illustrating the principles of a positive vibration suppression apparatus; 
     FIG. 2 is a view showing an oil hydraulic system of the positive vibration suppression apparatus; 
     FIG. 3 is a block diagram showing a signal generating circuit of the positive vibration suppression apparatus according to the present invention; 
     FIG. 4 is a block diagram showing an oil hydraulic system of the positive vibration suppression apparatus; 
     FIG. 5 is a plan view showing an embodiment of the invention, in which two vibration suppression apparatuses are disposed in perpendicular directions; 
     FIG. 6 is a plan view showing another embodiment, in which a vibration suppression apparatus for suppressing torsional vibrations is provided; 
     FIG. 7 is a view showing a further embodiment, in which vibration suppression apparatuses are arranged to permit simultaneous control of primary and secondary vibration components; and 
     FIGS. 8, 9 and 10 are a front view, a right side view and a plan view showing the appearance of the apparatus according to the present invention, respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2 is a schematic block diagram showing an oil hydraulic system of a positive vibration suppression apparatus according to the present invention. Acceleration gauges S1 and S2 are provided as vibration sensors on an active mass driver (AMD) 12 of the vibration suppression apparatus and a building 11, and a response signal is supplied to a control signal generating circuit 13. 
     The control signal generating circuit 13 effects phase control and amplification of the inputs as will be later described to produce a control signal which is supplied to a comparing circuit 14. Meanwhile, the sensor S1 which senses the movement of the AMD 12 also provides an output signal to the comparing circuit 14 for feedback control. The comparing circuit 14 supplies a control signal to an oil hydraulic servo valve 15 provided on an oil hydraulic cylinder 19 to control the oil hydraulic servo valve 15. The oil hydraulic system has a loop constituted by an oil hydraulic tank 16, an oil hydraulic pump 17, an oil hydraulic servo valve 15 and an oil hydraulic cylinder 19, and an accumulator 18 is provided between the oil hydraulic pump 17 and the oil hydraulic servo valve 15. 
     The oil hydraulic cylinder 19 can be operated under control by the oil hydraulic servo valve 15 to obtain a reaction force from the building 11 so as to apply a force tending to suppress vibrations of the building 11 to the AMD 12 of the vibration suppression apparatus. 
     FIG. 3 is a block diagram showing the control signal generating circuit. 
     In this embodiment, as shown in FIG. 3 to be described later, in addition to a main vibration suppression apparatus (shown at AMD1 in the drawing), an auxiliary vibration suppression apparatus (AMD2) is installed at an end of the building to control the torsional component of vibrations. In FIG. 3, an input 1 represents the acceleration of a weight of the main vibration suppression apparatus installed at the top center of the building as sensed by the sensor S1 shown in FIG. 6, inputs 2 and 4 represent the acceleration of the top center of the building as sensed by the sensor S2, and input 3 represents the acceleration of a weight of the auxiliary vibration suppression apparatus AMD2 installed at an end of the top of the building as sensed by the sensor S3, and an input 5 represents the acceleration of an end of the top of the building as sensed by the sensor S4. 
     The input 1 is passed through a low-pass filter 21 to remove very small vibration components and noise components, then amplified by a buffer amplifier 22 and then supplied through an integrating circuit 23 and also directly to a phase controller 24. Since the input 1 represents the acceleration, it is 90 degrees out of phase with respect to the velocity and also contains a mechanical time delay introduced in the mechanical part such as the oil hydraulic cylinder 19 (see FIGS. 2 and 8 to 10). Therefore, if necessary, it is subjected to 90-degree phase adjustment in the integrating circuit 23 and then to a phase control in a range of 0 to 90 degrees in the phase controller 24. Subsequently, its signal level is adjusted in an amplifier 25. 
     The input 2 likewise is subjected to removal of very small vibration components and noise components, then subjected to phase control and then passed through an automatic gain control circuit 26, thereby controlling its signal level to a preset level. The control signal is 90 degrees out of phase with respect to the phase of vibrations of the building. 
     The inputs 1 and 2 are combined through parallel amplifiers as noted above. 
     The driving of the weight 21 of the vibration suppression apparatus should be done within the capacity thereof, and the amplitude is limited, whereas there is a large acceleration range of the vibrations of the building 11 depending on the scale of earthquake. Therefore, an automatic gain control circuit (AGC) 26 is provided on the side of the building, so that the amplication factor of the building side circuit is high when the building side acceleration is low while it is low when the building side acceleration is high. Thus, while control 90 degrees out of phase with respect to vibrations of the building 11 is done according to the vibrations with a low building side acceleration, with increase of the building side acceleration the oil hydraulic cylinder 19 is no longer operative so that the weight 12 is just like stationary with respect to the building 11. With reduction of the building side acceleration the amplification factor of the building side circuit is increased again to reduce the period of attenuation of vibrations of the building 11. 
     The resultant signal obtained from the parallel amplifiers is also passed through a gain control circuit (AGC) 28 to obtain a preset signal level for controlling the movement of the weight 12 within the capacity of the apparatus. 
     The input 3, which represents the acceleration of the weight of the auxiliary vibration suppression apparatus AMD2, is controlled in an amplifier like the input 1 noted above. The inputs 4 and 5, which represent the accelerations of the center and end of the building, respectively, are passed through respective low-pass filters 21c and 21d and buffer amplifiers 22c and 22d before being supplied to a differential amplifier 30 to obtain their difference. The torsional vibration component is subjected to the same control as with the input 2 before being combined with the input 3 passed through the amplifier, and the resultant signal is passed through an automatic gain control circuit 28b to obtain a control signal with respect to the weight of the auxiliary vibration suppression apparatus AMD2. 
     FIG. 4 is a block diagram showing a single-system positive vibration suppression apparatus incorporating an oil hydraulic system according to the present invention. It uses a 4-ton weight 12 to suppress vibrations of a 400-ton building 11. 
     In this embodiments, a 200-V three-phase AC power source 41 is used to hold a 1.5-kW small size electric motor 42a operative at all time. Thus, a servo valve 15 is held in a controlled state at all time to continuously supply operating fluid at a rate of 2 to 3 liters per minute so that the apparatus is warmed up at all time. Further, an oil pressure is stored in the accumulator 18 (80 liters) by the 1.5-kW small size electric motor 42a and a small size pump 17a connected thereto, and operating fluid necessary in an initial stage of an earthquake is supplied from this accumulator. Thus, a satisfactory initial control state can be obtained. Further, when the oil pressure in the accumulator 18 is reduced with the start of the 15-kW large size electric motor 42 at the time of occurrence of an earthquake, the operating fluid is supplied from the large size pump 17 connected to the 15-kW large size motor 42. 
     The accumulator 18 is provided with a pressure switch as pressure sensor means. When the pressure rises at the time of the start of control, a pressure control valve 43 is controlled to cause circulation of oil between the large size pump 17 and the tank 16 (see FIG. 2) so as to keep the load on the 15-kW large size electric motor minimum. When the oil hydraulic pressure is reduced to a predetermined pressure, the pressure regulator valve 43 is opened to the side of the oil hydraulic control circuit to control the pressure of operating fluid flowing from the large size pump 17 connected to the 15-kW large size electric motor 42. Thus, the load on the 15-kW large size electric motor is controlled to save power consumed by the motor. The 15-kW large size electric motor 42 is held warmed up in an idling state with a small load while the operating fluid is circulated between the large size pump 17 and the tank 16. 
     The vibration suppression apparatus described above effects vibration suppression as follows. 
     The sensor 2 senses vibrations of the building 11 and supplies a response signal to the control signal generating circuit 13. The control signal generating circuit 13 provides a control signal to the servo valve 15 and power source 14 to start control of the hydraulic pressure and servo valve 15. At the same time, the switch SW1 of the large size electric motor 42 is closed. 
     Meanwhile, the sensor S1 senses the movement of the weight 12 as additional mass with the operation of the oil hydraulic cylinder 19 and supplies a response signal to the control signal generating circuit 13. Weight 12 may be connected to hydraulic cylinder 19 by any conventional rigid coupling means 19a. 
     As the principles of the vibration suppression, the vibrations of the building body 11 can be controlled by applying a force tending to cause converse vibrations. In this case, the control circuit 13 controls the phase of mechanical time delay due to friction and other causes and supplies a control signal to the servo valve 15. Further, error correction is effected by feeding back the movement of the weight 12. 
     When the vibration control is started, the pressure regulator valve 43 senses a pressure reduction in about 5 seconds, for instance, and the oil hydraulic control is continued through control of the load of the large size electric motor 42. 
     FIGS. 8 to 10 show the construction of the active mass driver in a preferred embodiment of the positive vibration suppression apparatus according to the present invention. The weight 12 has a substantially channel-shaped side view, and it is suspended from an upper steel frame 54. It is suspended at eight points via upper and lower pulleys 55 and hanging media 56 such that it extends horizontally and is capable of movement relative to the building body 11. In the horizontal direction, the weight 12 is connected to the building body 11 by the oil hydraulic cylinder acting 19 as an actuator. The oil hydraulic cylinder 19 is operated for expansion and contraction according to an instruction from a control mechanism to apply a control force to the building body 11. 
     The weight 12 has the channel-shaped outer shape in order to install the oil hydraulic cylinder 19 in the depression, thus reducing the installation space and obtaining a compact construction. Further, it is possible to let the pulley hanging point, centroid of the weight 12 and pressure application point of the oil hydraulic cylinder 19 to coincide with one another, which is convenient for the design. 
     Buffering members 58 are attached to the lower surface of the weight 12 at four points, so that the apparatus can be protected against an accident such as occasional breakage of the hanging media 56. The lower end of the weight 12 is guided by four guide members 59 to prevent twisting of the movement of the weight 12. 
     FIG. 5 shows an embodiment consisting of two perpendicular vibration suppression apparatuses disposed on the top of the building to provide control in two, i.e., X- and Y-, directions of the building. In FIG. 5, the vibration suppression apparatus in the X-direction is a main vibration suppression apparatus AMD1, and the apparatus in the Y-direction is an auxiliary vibration suppression apparatus AMD2. Vibrations in all directions can be controlled through control of the two perpendicular vibration suppression apparatuses AMD1 and AMD2. Designated at S1 to S4 are acceleration gauges as vibration sensor means. 
     FIG. 6 shows another embodiment consisting of two vibration suppression apparatuses provided at the center and an end of the top of the building and extending in the same direction. The central apparatus AMD1 is a main apparatus for effecting main control, and the apparatus AMD2 at the end is an auxiliary apparatus for controlling the torsional vibration component. This embodiment is suited for control of an eccentric building. 
     FIG. 7 is a further embodiment of the apparatus for a high story building. The primary vibration component is controlled by the vibration suppression apparatus AMD1 provided at the top of the building. The secondary vibration component is controlled by the vibration suppression apparatus AMD2 provided on a story corresponding to the node of the secondary vibration mode.